Carburetor



March 4, 1947.

M. lg. CHANDLER CARBURETOR 'Filed Sept. 14, 1943 INVENTDR MUD/v E. D15/yan? AGENT Patentedl 4, 1947 UNITED STATES PATENT ori-'lcs CARBURETOR .Milton E. Chandler, New Britain, Conn., assignor. by mesne assignments, toNiles-Bement- Pond Company, West Hartford, Conn., a corporation of New Jersey Application September 14, 1943, Serial No. 502,266 claims. (ci. 2er-e9) The present invention relates to carburetors for use with internal combustion engines on aircraft. .f

In certain types of aircraft carburetors it is customary to measure the quantity of air entering the engine and to control the quantity of fuel supplied to the engine in accordance with the quantity of air so as to maintain a fuel to air ratio which provides predetermined combustiony conditions in the engine. The usual method of measuring the air flow is to utilize a Venturi meter. Meters of this type measure the velocity of the flowing air, and are therefore subjectto error when the density of the air changes. When such a meter is used on an aircraft, the variation in air density with altitude must be considered in the design of the carburetor, and some means must be provided to compensate for it.

One of the most effective types of altitude compensating arrangements involves the use of a sealed flexible bellows exposed to atmospheric pressure which expands and contracts inf-'accordance with the difference between the internal and external pressures acting on it. Such a bellows may be used to operate a valve or other controlling member to produce a. compensating effect either in the air meter or in the fuel flow control mechanism.

Such bellows may be evacuated substantially completely, or they may be filled with fluid. Fluid filled bellows may be classified in three types:

(l) ABellows filled with fluid at less than atmospheric pressure, commonly called vacuum-filled bellows, so that when normal atmospheric pressure conditions exist outside the bellows, it is stressed in a sense tending to cause contraction of the bellows;

(2) Bellows filled with fluid at substantially normal atmospheric pressure, commonly called atmospheric-filled bellows, so that when normal pressure exists outside the bellows, it is unstressed; and

(3) Bellows filled with fluid under a pressure greater than atmospheric, commonly called presl sure-filled" bellows, so that when normal atmospheric pressures exist outside the bellows, the bellows is stressed in a direction tending to expand it. Y

The fluid with which such a bellows is filled may bechosen to have a suitable temperature coeillcient of expansion so that the bellows responds to variations in temperature of the surrounding p air as well as to variations in pressure.

A bellows of this type is a relatively delicate structure, and when used on an aircraft where it is subject to considerable vibration, it has been spite all possible precautions. When such a leak occurs, the internal and external pressures acting on the bellows are equalized. Therefore a bellows filled with fluid under less than atmospheric pressure expands when it leaks whereas a. bellows filled with fluid under greater than atmospheric pressure contracts when it leaks. A bellows filled with fluid at normal atmospheric pressure, on the other hand, tends to return to its normal position when it leaks regardless of existing external pressure,

When such a bellows is used to compensate for altitude on an aircraft carburetor, it is essential that the bellows be so arranged, that it will not tend to cause a leaning out of the fuel and air mixture when the bellows leaks. If the fuel and air mixture is made toc lean, the motortends to overheat, with consequent damage to the motor. It is therefore usual to provide a bellows of the type filled with fiuid at normal atmospheric pressure for use in compensating the action of an aircraft carburetor for altitude variations.

Since with 1vacuum filled bellows a wider range of temperature and pressure response character istics are available than with the atmospheric filled type, it is desired to use bellows of the vacuum-lled type in aircraft carburetors.

It is therefore an object of the presentinvention to provide an altitude compensating arrangement for an aircraft carburetor wherein a bellows filled with fluid at a pressure different from atmospheric is used, and wherein means is provided to insure that upon leakage of the bellows, the fuel and air mixture supplied to the engine is made richer, rather than leaner.

Another object is to provide an arrangement including a flexible bellows for compensating the action of an aircraft carburetorfor changes in altitude and further including means to insure that upon failure of the bellows the altitude compensating means is rendered inoperative in a, safe sense.

Another object is to provide iiuid fiow control apparatus including a vacuum filled bellows and valve means operated thereby in a closing direction upon expansion of said bellows, and means whereby upon abnormal expansion `of said bellows. the valve means is opened.

Other objects and advantages of the present invention will become apparent from a consideration of the appended specification, claims and drawing, in which the single figure is a somewhat titude compensation purposes and embodying the principles of my invention.

internal springs such l I for air flowing thru an aircraft carburetor. Air

22, another expansible chamber 23 in the pressure meter 2I, a conduit 24. a chamber 25 and a conduit 28 to the throat of Venturi restriction I2.

The flow of air from conduit 24 into chamber 25 is controlled by a valve 25 which is mounted on the free end of a flexible bellows 21, whose opposite end is iixed inside the chamber 25. Another bellows 28 is mounted in the chamber 25, and the interiors'` of the two bellows are connected thru a conduit 30. The bellows 21 and 28 are filled with an expansible fluid at a pressure less than atmospheric, so that when the pressure in the chamber 25 is at the normal atmospheric value, the bellows 21 and 28 tend to collapse. If the bellows themselves are not suiiiciently strong to prevent such collapse, they may be provided with as the springs .3| and 32 illustrated in the drawing.

,The total pressure drop between the inlet II and the throatof the venturi I2 may be separated into two components, one appearing across restriction 22 and the other across valve 26. As the altitude of the aircraft increases, the bellows 21 and 28 expand. Expansion of bellows 21 moves valve 25 in a closing direction thereby restricting the ow of lair thru the second passage previously traced. As the valve 25 is moved toward closed position with increasing altitude, a greater proportion of the total pressure drop takes place across valve 25 and a smaller proportion across restriction 22. It is this pressure drop across restriction 22 which is effective in the pressure meter 2l as a measure of the mass of the ilowing air. The function of bellows 21 and valve 26 is to maintain a pressure diierential between chambers 20 and 23 of pressure meter 2l which is substantially a true indication of the mass of air owing thru the passage I8.

Since the pressure differential produced by a Venturi restriction varies with the velocity .-)of theI air, it may be seen that, for a constant mass of air ilowing per unit time. a decrease in density of the air causes the venturi to create a higher differential pressure. In order to secure a differential pressure which is an accurate measure of the mass of air owing, the bellows operated valve 25 is provided, and it responds' to a decrease in air-'density so as to reduce the proportion of the total pressure drop between the inlet II and the throat of Venturi restriction I2 which is used as a measure of the mass of the flowing air in the pressure meter 2|.

If the bellows 21 leaks, its internal and external pressures become equalized, and it expands, closing the valve 26 completely. This would result in the absence of any pressure drop across restriction 22, and the pressure meter 2I could no longer operate in accordance with the mass of the flowing. air. unless means 'were provided to prevent such action.

I have, however, provided means to prevent the occurrence of such a condition. A conduit 33 leads from the conduit 24 and thru an opening controlled by a valve 34, biased to closed position by a spring 35, into the chamber 2li.v A projection 38 on the valve 34 extends into the path of movement of the free end of bellows 28 in the chamber 25. It may be seen that upon expansion of bellows 21 and 28 such as accompanies a leakage of either bellows, the projection 36 is engaged by the free end of bellows 28, and the valve 34 is thereby opened against the force of spring 35. Under such conditions, the pressure drop appearing across restriction 22 is a iixed proportion of the total pressure drop between the inlet II and the throat of venturi I2, depending upon the relative proportions of restriction 22 and the open- 4 ing controlled by the valve 34. These openings may be so designed as to produce any desired fuel to air ratio under sea level conditions. If the fuelto air ratio is sufficiently rich under sea level conditions, the mixture will become increasingly rich with altitude, so that altho the altitude compensation arrangement is inoperative it fails in a safe sense, in that the mixture is always richer than necessary.

The bellows 28 and spring 32 should be so designed that the combination has a relatively high spring rate as compared to that of bellows 21 and spring 3|. so that the motion of the free end of bellows 28`with changes in external pressure is small compared to the motion of the free end of bellows 21. Undesired interference between projection 38 and the end of bellows 28 is thus prevented.

The fuel flowing thru the carburetor of Figure j 1 comes from a pump or other source of fuel under pressure (not shown) From this source, the fuel iiows thru a conduit 31, a fuel regulator valve 38, a mixture control unit 40, a jet system 4I, past an idle valve 42, and thru a pressure- .regulator 43 and a conduit 44 to the discharge nozzle I4.

The fuel regulator 38 includes a casing divided -by a iiexible diaphragm 45 into a pair of ex' A conduit 52 conducts fuel from the fuel regulator 38 to the mixture control unit 48. The mixture control unit 40 includes a disc valve 53 rotatable by means of a shaft 54 to open and close ports connected to conduit 52 and to a pair of conduits 55 and 56 extending to the jet system 4I'. When the disc valve member 53 is in the position shown in the drawing, fuel may enter the jet system 4I only thru the conduit 55. The mix ture control valve is then said to be in its lean position. If the mixture control valve is rotated so that both the conduits 55 and 56 are open, the mixture control valve is said to be in its rich position, If the valve 53 is rotated so thatboth conduits 55 and 55 are closed, the mixture control is said to be in its cut-off position.

Fuel entering the jet system 4I thru the conduit 55 may iiow either thru a fixed restriction or jet 51 orthru a restriction or jet 58 controlled by a poppet valve B8 biased to closed position by means of a spring 5I. Fuel entering the Jet system 4I thru the conduit 55 flows thru a xed restriction 52. Fuel flowing thru the restrictions 58 and 52 passes thru an additional limiting restriction 83 before passing out of the jet system thru a conduit 64.

The pressure regulator 43 includes a casing divided by a flexible diaphragm 65 into a pair of expansible chambers 66 and 61. The diaphragm 65 carries at its center a valve 68, which is biasedy toward closed position by a spring 10. Altho the valve 68 is illustrated as beingbalanced against outlet pressure, it is not necessary that a balanced valve be used when the fuel flow is controlled by a pressure meter such as that indicated at 2|, as explained hereinaftera The chamber 66 is connectedvthru a conduit 1| and the conduit |8, vent ring I1 and the impact tubes I6 to atmospheric pressure at the inlet Il. This connection is merely to permit free movement of the diaphragm 65 without compressing the uid in the chamber 66. Since the chamber 66 is supplied with air at atmospheric pressure, the spring acts to maintain a pressure greater than atmospheric in the chamber 61. The fuel supplied to the discharge nozzle |4 is therefore always under pressure and any tendency of the' fuel to vaporize in the conduit 44 or in the nozzle |4 is minimized.

The pressure meter 2| includes a casing divlded by three `flexible diaphragms 12, 13 and 14 into four expansible chambers 15, 20, 23 and 16l The connections of chambers 28 and 23 have already been described. The chamber is connected thru a conduit 11 to the conduit 64 in the fuel line downstream from the jet system 4|. The chamber 16 is connected thru-a conduit 18 to the chamber 46 in the fuel regulator 38.

A portion of the fuel entering chamber 41 of the fuel regulator 38 passes thru restriction 5|,

chamber 46, conduit 18, chamber 16 of pressure meter 2|, and thru a conduit 80 to a drain in the air passage I8.

The pressure meter 2| also includes a Valve member 8| attached to the diaphragms 12, 13, and 14, and biased to closed position by a spring 82.

The valve 8l controls the pressure in chamber 16 and hence the pressure in chamber 46 of fuel regulator 38. y

It may be seen that upon an increase in the quantity of air flowing thru the passage I0, the pressure differential between chambers 28 and 23 is increased, thereby moving the valve 8| in a closing direction and increasing the pressure in chamber 16, .The closingmovement of valve 8| continues until the pressure in chamber 16 has increased suiciently to balance the increase in the force acting on diaphragm 13 due to the increased air pressure differential.

'I'he increased pressure in chamber 16 is transmitted to chamber 46 of the fuel regulator 38,

where it acts on diaphragm 45 in a direction to open the valve 48 and increase the ow of fuel lto the carburetor so as to maintain' the desired fuel to air ratio.A

The quantity of fuel entering the carburetor is determined by the pressure differential across the jet system 4|. The pressure upstream from the jet system is regulated by the fuel regulator 38 in accordance with the quantity of air entering the carburetor, in the manner just described. If the pressure downstream from the jet system 4| varies, that variationis communicated thru conduit 11 to the chamber 15 in pressure meter 2|, where it acts on the valve 8| in a direction to produce a balancing change in the pressure upstream from the jetsystem 4| For example, if the pressure downstream from the jet system decreases for any reason, the decrease in pressure is communicated to chamber 15," causing an opening movement of valve 8|, thereby decreasing the ing a closing movement of valve 8| and a decrease in pressure upstream from the jet system 4| The spring loaded valve 48 controlling the fuel rw thru restriction 58 is provided to increase the fuel and air ratio whenever the pressure differential across the jet system exceeds a value deter mined by the strength of spring 6|. This increase in the fuel to' air ratio causes the engine to run on a rich mixture whenever high'power output is required of the engine.

When the throttle I3 is at closed or nearly closed positions, the quantity of air iiowing thru the Venturi restriction I2 is so small in proportion to its cross-sectional area that the pressure differential produced in the chambers 20 and 23 of the pressure meter 2| is no longerv an accurate -measure of the quantity of air entering the enposition, At normal -open throttle positions, the idle valve 42 is retracted so that itidoes not restrict the fuel flow. When the throttle position is such that the pressure meter 2| is no longer accurate, the idle valve 42 is moved to restrict the fuel flow. In effect, the control of the fuel flow is transferred from the pressure meter 2| to the idle valve 42 at low air-flows.

I claim as my invention:

1. In a carburetor for an internal combustion engine, in combination, a first conduit for air flowing to said engine for combustion purposes, means associated with said first conduit for producing two unequal pressures whose difference is a function of the velocity of the air owing therethru, a second conduit in which a flow of air is produced by said unequal pressures, a fixed re striction in said second conduit, a pairyof valves connected in parallel in said second conduit. spring means biasing one o1' said valves to closed position, means including a first flexible bellows for operating the other of said valves so as to produce across said fixed restriction a pressure differential substantially proportional to the mass of air flowing thru said first conduit, said flexible bellows having its exterior exposed to a pressure varying in accordance with atmospheric pressure and containing an expansible iiud at a pressure substantially less than said exterior pressure so that the dierence between said exterior and lnterior pressures tends to contract said bellows and open said other valve, a second bellows having its interior connected to the interior of said first bellows and normally spaced from said one valve, but effective upon expansion such asv accompanies bellows leakage to engage and open said one valve against said biasing means, and means responsive to the pressure diiferential across said 'fixed restriction for controlling the flow of fuel to said engine.

' 2. In -a carburetor for an internal combustion engine, in combination, a first conduit for air fiowing to said engine for combustion purposes, means associated with said rst conduit for producing two unequal pressures whose difference is a function of the velocity of the air owing therethru, a second conduit in which a flow of air is produced byl said unequal pressures, a fixed restriction in said second conduit, a pair of valves sible iiuid at a pressure substantially less than said exterior pressure so that the difference between said exterior and interior pressures tends to c' ntract saidbellows and open said other valve, firs spring means associated with said bellows and acting in a closing direction'on said other valve, said spring means being effective upon leakage of said bellows to close said other valve,.a

second bellows having its interior connectedto,

the interior of said rst bellows. and aligned with but normally spaced from said one valve, second vspring means associated with said secondbellows and having a rate sufficiently high to limit the travel of said second bellows under normal con-A ditions so that said one valve is not engaged by said second bellows, said second bellows being effective upon expansion such as accompanies bellows leakage to engage and open said one valve against its associated biasing means, and means responsive to the pressure differential across said fixed restriction for controlling the flow of fuel to said engine.

3. In a carburetor for an internal combustion engine, an air conduit, means responsive to the rate of flow of air thru said conduit for controlling theiiow of fuel to said engine, and means for varying the flow of air thru said conduit to correct the fuel ow for variations in air density, said last-named means comprising a pair of valves connected in parallel in said conduit, spring means biasing one of said valves to closed lposition, means including a first fiexible bellows for operating the other of said valves, said flexible bellows having its exterior exposed to a fluid under pressure varying in accordance with atmospheric pressure and containing anexpansible iiuid at a pressure substantially less than said exterior pressure so that a decrease in the difference between said exterior and interior pressures tends to expand said bellows and close said other valve, and a second bellows having its interior connected to the interior of said first bellows and aligned with but normally spaced from said one valve, but effective upon expansion such as accompanies bellows leakage to engage and open said one valve against said biasing means.

4. In a carburetor for an internal combustion engine, an air conduit, means responsive to the rate of iiow of air thru said conduit for controlling the flow of fuel to said engine, and means for varying the iiow of air thru said conduit to correct the fuel flow for variations in air density,

said last-named means comprising a pair of valves connected in parallel in said conduit, spring means biasing one of said valves to closed position, means including a first iiexible bellows for operating the other of said valves, said flexible bellows having its exterior exposed to a i'luid under pressure varying in accordance with atmospheric pressure and containing an expansible fluid at a pressure subtantially less than said exterior pressure so that a decrease in the diilerence between said exterior and interior pressures other valve, said spring means being effective upon leakage of said bellows to close said other valve, a second bellows having its interior connected to the interior of said 'first bellows and aligned with but normally spaced from said one valve, and second spring means associated with said second bellows and having arate sufficiently high to limit the travel of said second bellows under normal conditions so that said one valve is not engaged by said second bellows, said second bellows being effective upon expansion such as accompanies bellows leakage to engage and open said one valve against its associated biasing means.

5. In a carburetor for an internal combustion engine, in combination, a, first conduit for air flowing to said engine for combustion purposes, means associated with said iirst conduit for producing two unequal pressures whose difference is a function of the velocity of the air flowing therethru, a secondv conduit in which a flow of air is produced by said unequal pressures; a xed restriction in said second conduit, a pair of valves connected in parallel in said second conduit, spring means biasing one of said valves to closed position, means including a flexible bellows for operating the other of said valves so as to produce x across said fixed restriction a pressure differential substantially proportional to the mass of air flowing thru said first conduit, said iiexible bellows having its exterior exposed to a iiuid under pressure varying in accordance with atmospheric pressure and containing an expansible llid at a pressure substantially less than said exterior pressure so that a. decrease in the diierencebetwe'en said exterior and interior pressures tends to expand said bellows and close said other valve, means for opening said one valve against A'said biasing means including a member associated with said bellows for concurrent movement 4therewith and normally spaced from said one valve to permit independent movement of said member and said one valve during the normal range of movement of said bellows but eective upon extreme expansion of. said bellows such as accompanies bellows leakage to engage and open said one valve against said biasing means, and means responsive to the pressure differential across said fixed restriction for controlling the flow of fuel to said engine.

' MILTON E. CHANDLER.

REFERENCES `errar The following references are of record in the file of this patent: 1

UNITED STATES PA Y '-fl 

